Of all Andy Murray's many achievements, becoming the first British player ever to be ranked world singles number one is possibly the most impressive.
To sit at the top of the standings in an era dominated by three of the greatest players of all time is something even the man himself felt was unlikely until not long ago.
Between them, Novak Djokovic, Roger Federer and Rafael Nadal have hogged top spot for almost 13 years.
As recently as June, when Djokovic became the first man in 47 years to hold all four grand slam titles at the same time, the Serbian's lead appeared unassailable.
But Murray has been imperious in the months since, winning Wimbledon, Olympic gold and five other titles and losing just three matches.
His path to the summit has, of course, been helped by outside factors.
If the French Open was the high point of Djokovic's career, the aftermath was a feeling of burn-out and loss of motivation that led to a significant dip in his level.
Federer and Nadal, meanwhile, have been taken out of the equation by injury, with Murray not having to face either since May.
But it would be tough to find anyone in tennis who begrudges Murray his place at the top of the tree.
The 29-year-old is the oldest first-time number one since John Newcombe in 1974, a year after the rankings system was put in place.
Murray has been relentless in trying to wring every last drop out of his talent and never afraid to make bold decisions.
One of those was appointing Ivan Lendl as his coach ahead of the 2012 season, leading to his first two grand slam titles, and it is no coincidence his second great period sees Lendl in his corner once again.
But the signs were there to a degree before Murray lured the eight-time grand slam champion away from his home in Florida and back on tour.
Despite not winning a grand slam title, last year was arguably the best of his career until 2016, with his consistency helping him finish a season ranked number two for the first time.
A blip following the birth of Murray's daughter Sophia in February was followed by a brilliant clay-court season, including victory over Djokovic in the final of the Rome Masters and a first final appearance at the French Open.
The Scot's second serve, previously his biggest weakness, was much improved along with his forehand while the two years he spent with Amelie Mauresmo helped him rediscover the natural variety in his game.
The extra belief only Lendl appears able to give him was the last piece of the puzzle and, following their reunion, he went on a career-best 22-match unbeaten run that took in a second Wimbledon title and Olympic gold.
If Murray's 2013 Wimbledon triumph and the dramatic finale to his win over Djokovic will surely remain his defining moment, this year's success was a demonstration of his supreme talents.
Aside from a tense quarter-final against Jo-Wilfried Tsonga, Murray was never troubled and dominated first-time slam finalist Milos Raonic in a way Federer and Djokovic have previously done to him.
There was nothing straightforward about his victory over Juan Martin del Potro in Rio but in taking gold he claimed a piece of tennis history for himself - the first player ever to win two singles titles.
Even then, overtaking Djokovic this year seemed virtually impossible, but Murray has been relentless, closing in swiftly as successive titles in Beijing, Shanghai and Vienna put number one on the line in Paris, where Murray beat John Isner in the final.
Losing top spot could be just the spark Djokovic needs to reignite the fire, and his record at the ATP World Tour Finals, with four titles in a row, means Murray faces a big fight to hold on to it for longer than a fortnight.
But, whoever sits on top of the tree at Christmas, Murray is reaping richly-deserved rewards and there may yet be plenty more to come.
Source: PA
